Method for adjusting drilling of drilling machine and rock drill

ABSTRACT

A method for adjusting percussion pressure and a drilling machine. In the method the percussion power of a drilling machine is adjusted by moving a shank in the longitudinal direction of the drilling machine forwards when a smaller percussion power is to be transferred from the percussion piston to the shank. The drilling machine comprises at least two groups of pistons moving in the axial direction of the drilling machine, the pistons being connected to act on the shank by means of a pressure medium acting behind the pistons towards the front end of the drilling machine. The drilling machine comprises at least two separate groups of pistons whose travel with respect to one another is different and where pressure medium channels separate from one another lead to the cylinder spaces of both piston groups.

BACKGROUND OF THE INVENTION

The present invention relates to a method for adjusting drilling of adrilling machine in a drilling machine comprising a frame, a percussionpiston arranged to the frame and moving in the longitudinal direction ofthe frame, an absorber situated in the front end of the travel of thepiston portion of the percussion piston, a shank situated in the axialextension of the percussion piston and at least two pistons arranged tothe frame moveable in its axial direction, the pistons being situated inaxial cylinder spaces formed around the shank and arranged to act on theshank and push it towards the front portion of the drilling machine bymeans of a pressure medium acting on the rear surface of the pistons,whereby at least during drilling such a pressure of pressure medium isset to act on the rear surface of the pistons that the total force ofall the pistons acting on the shank and pushing it forwards exceeds feedforce acting on the drilling machine during drilling, wherefore some ofthe pistons are pushed to the foremost position of their travel by meansof the pressure medium, whereby the shank is at its optimal percussionpoint when being supported by them.

The present invention also relates to a drilling machine which drillingmachine comprises a frame, a percussion piston arranged to the frame andmoving in the longitudinal direction of the frame, an absorber situatedin the front end of the travel of the piston portion of the percussionpiston, a shank situated in the axial extension of the percussionpiston, and an axial bearing arranged to the frame for receiving axialforces directed to the frame via the shank, which axial bearing isformed of at least two pistons which are placed in the frame into axialcylinder spaces formed around the shank and arranged to act on the shankand push it towards the front portion of the drilling machine by meansof a pressure medium acting on the rear surface of the pistons, wherebyat least during drilling such a pressure of pressure medium is set toact on the rear surface of the pistons that the total force of all thepistons acting on the shank and pushing it forwards exceeds the feedforce acting on the drilling machine during drilling and whereby thetravel of some of the pistons towards the front portion of the drillingmachine is restricted in such a manner that when said pistons are intheir foremost position, the shank is essentially situated at itsoptimal percussion point when being supported by them.

When drilling holes with a rock drill, drilling conditions vary invarious ways and in some situations it is necessary to be able to adjustfast and effectively the percussion power of the rock drill or otherfactors having an effect on drilling. In prior art solutions, percussionpower is adjusted by adjusting the pressure of the pressure fluid in thepercussion machinery, which is, however, quite difficult to realizeaccurately and in a controlled manner. Further, in prior art solutions,the position of the shank with respect to the percussion piston isalways to be kept at a certain so-called optimal percussion point whereas great a portion of percussion power as possible moves to the shankand via the shank through the drill rod to the drill bit. Finnish Patent84,701 discloses a solution where the position of the shank is set byusing several pistons, the pressure acting on which together pushes theshank into an optimal percussion point, but allows it to move backwardsby means of a strong return pulse and to receive thus the stresscreated. In said Finnish Patent some of the pistons can also movefarther than the others towards the front end of the drilling machineand thus follow that shank, whereby they receive the return movement andabsorb it at an earlier stage during the return pulse.

SUMMARY OF THE INVENTION

In prior art solutions, the adjustment of drilling is difficult and theobject of this invention is to provide a method and drilling machinewhere drilling can be easily adjusted as desired. The method accordingto the invention is characterized in that the pressure acting on atleast some of the pistons is adjusted for providing a desired drillingsituation.

The drilling machine according to the invention is characterized in thatit comprises at least two pistons, pressure channels separate from oneanother leading to the pressure spaces behind the pistons and means forfeeding pressure fluid to the pressure spaces behind the pistons in sucha manner that a pressure is acting on them irrespective of one another.

The essential idea of the invention is that drilling is adjusted byadjusting the position of the shank with respect to the optimalpercussion point and the force on the shank when it deviates from itsoptimal percussion point. In that case, in the adjustment of thepercussion power, a desired amount of power is transferred via the shankto the drill rod and the remaining portion of the power is absorbed bythe absorber in the front end of the travel of the percussion piston.Similarly, when rock contact of a drill bit is to be adjusted, thepressure acting behind the pistons is kept such that a smaller pressurethan feed force is behind the pistons which are capable of movingforwards from their optimal percussion point, the pressure beingvariable according to the number of drill rods used in long holedrilling in such a manner that at the arrival of a percussion pulse, thedrill bit can always be kept as desired in contact with the rock to bedrilled without any essential power loss to the absorber. The method canbe realized most simply by using several pistons with different travel,the travel of the pistons to the front end of the drilling machine beingappropriately restricted. In that case, when feeding a pressure fluid ofa suitable pressure behind pistons with different travel, the shank canbe moved forwards as desired. An advantage of the invention is that byusing pistons moveable to different travel, the shank can be movedmechanically into a desired percussion point that is either the optimalpercussion point or one deviating from it. Because the position of thepercussion point is precisely determined for all situations, powertransfer and thus the percussion power of the machine can be calculatedaccurately and dimension it according to desired properties duringmanufacturing. The adjustment of drilling is fast and simple as it canbe realized only by adjusting the pressure of pressure fluid acting onthe pistons that support the shank.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be explained in more detail withreference to the appended drawings, in which

FIG. 1 shows a schematic view of one construction in a drilling machinesuitable for realizing the method according to the invention,

FIG. 2 shows a schematic, sectional view of the adjustment of thedrilling machine according to FIG. 1 in different power adjustmentsituations,

FIG. 3 shows a schematic, sectional view of a second construction in adrilling machine suitable for realizing the method according to theinvention,

FIG. 4 is a graphical illustration which shows a schematic, sectionalview of forces caused by pressures present in connection with onerealization of the method according to the invention, and

FIG. 5 shows a schematic view of a third construction in a drillingmachine suitable for realizing the method according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of a drilling machine comprising apercussion piston 1 and a shank 2 situated coaxially with the percussionpiston. The shank 2 is rotated in a manner known per se by means of arotation motor (not shown) by rotating a bushing 3 around the shank 2which can move in the axial direction with respect to the bushing. Thebushing 3 supports the shank 2 on a slanted supporting surface 3 a thatis in contact with a corresponding slanted supporting surface 2 a of theshank. There are several pistons 4 a and 4 b behind the bushing 3connected to or indirectly acting mechanically on the rear surface ofthe bushing 3. A restricting ring 5 is disposed around the bushing 3restricting the movement of the pistons 4 a and 4 b towards the frontend of the drilling machine. The pistons 4 a and 4 b are situated incylinder spaces which have been drilled to the frame 6 and which areparallel to the axis of the percussion piston 1 and pressure fluidchannels 7 a and 7 b lead to the cylinder spaces. There are severalpistons 4 a and 4 b in the frame 6 of the drilling machine and they aredivided into groups in such a manner that there are at least twoseparate groups whose travel towards the front end of the drillingmachine is different. This construction is described in more detail inFinnish Patent 84,701, the contents of which are considered to beincluded in the specification of the present application. Further, thedrilling machine comprises an absorber 8 in the front end of thecylinder space of the percussion piston 1, that is, in the travel of thepiston portion 1 a of the percussion piston 1 in the front end of thedrilling machine and the front end of the piston portion 1 a strikes theabsorber when the percussion piston for some reason should strike pastits normal optimal percussion point. This construction is generallyknown per se and used to stop the drilling machine from becoming brokenand therefore it is not explained in more detail herein.

By means of the method according to the invention, the position of theshank of the drilling machine and thus e.g. percussion power or rockcontact of the drill bit can be adjusted by using this construction.This takes place so that during normal drilling the pressure fed behindthe pistons is kept such that the pistons push the shank to its optimalpercussion point, but cannot push it any farther as the power caused bypistons 4 b with longer travel via the bushing 3 to the shank 2 issmaller than the feed force of the drilling machine. During the stroke,when the body of the drilling machine does not have time to move withthe drill rod, the pistons follow the shank and thus support the drillbit against the rock by the pressure of the force set to act on them,until the drilling machine has had time to move. When the percussionpower is to be diminished, at least such a pressure of the pressurefluid is fed behind the pistons 4 b that the pistons 4 b with longertravel are able to push the shank their allowed travel forwards, wherebythe percussion piston 1 strikes the shank 2 later than usual and thussome of its percussion energy is absorbed in the absorber 8 of thepercussion piston. When three different percussion powers, for example,are to be used, three piston groups with a different percussion lengthare also used, whereby by appropriately feeding pressure behind thepistons, the shank can be moved to a desired power transmissionposition.

FIG. 2 shows a schematic view of the adjustment of percussion power inanother way. In this case, pistons with different travel, which areindicated by numerals 4 a to 4 d, are each connected to a specific groupand to a specific feed channel 7 a to 7 d of pressure fluid separatefrom other piston groups. In the figure, one piston 4 a, 4 b, 4 c and 4d, respectively, refers schematically to all pistons of one group. Thefigure also shows schematically by numerals 5 a to 5 d the portions ofthe restricting ring 5 that restrict the travel of different pistons 4 ato 4 d in different ways. Similarly, the figure also shows with brokenlines La to Ld the travel which each piston or piston group can movewith respect to one another and broken line La describes the positioncorresponding to the optimal percussion length of the shank and lines Lbto Ld positions corresponding to the transfer of pistons 4 b and 4 cthat have moved forwards with respect to the optimal percussion pointwhere the piston portion 1 a of the percussion piston 1 strikes ashorter or a longer distance, respectively, to the absorber 8 or thepercussion piston has otherwise moved away from its optimal percussionpoint. When the cross section of the pistons with respect to thehydraulic pressure to be used is dimensioned appropriately, a pressurefluid Pa to Pd with a different pressure can be fed behind each pistongroup independently of the others and then it can be easily selectedwith which travel of the pistons 4 a to 4 d the percussion point of theshank is to be set. Correspondingly, this can be attended to bymaintaining the same pressure behind all pistons, whereby by selectingappropriately the area and the number of pistons and by adjusting theactive pressure, the desired forces are obtained for the desired pistongroups.

The adjustment of percussion power is carried out automatically byadjusting the values of the pressure of the pressure fluid acting behindthe pistons 4 a to 4 d suitable ones with respect to the feed force ofthe drilling machine. In that case, if the penetration of the drillingtool is for some reason, e.g. because of poor rock material or the like,greater than the feed speed, the shank moves because of the pressureacting behind the pistons 4 a to 4 d forwards to a position where thepercussion point is no longer optimal. Depending on behind which pistonspressure of pressure fluid is fed or how great a pressure is set behindthe pistons, the shank either moves somewhat forwards from its optimalpercussion point, but only such a distance so that the percussion pistondoes not strike the absorber or, if it moves the distance specified bythe pistons 4 c and 4 d, it partly strikes the absorber 8. The fartherthe shank can penetrate, the smaller the transfer of percussion powerwill be between the percussion piston 1 and the shank 2. When startingdrilling or with certain types of rock or when the conditions thusrequire, transfer capacity can be selected by using sufficient pressurebehind a desired piston group 4 a to 4 d or behind all groups, whereby asufficiently small percussion power is provided for each differingdrilling situation.

FIG. 3 shows a schematic view of a second construction in a drillingmachine suitable for realizing the invention, whereby correspondingparts in FIG. 3 are referred to by the same numerals as in FIG. 1. Inthe embodiment shown in FIG. 3, bushing-like pistons are used instead ofseveral separate pistons and the bushing-like pistons are placed aroundthe percussion piston coaxially with it. In this case, pistons 14 a and14 b are placed in such a manner that the piston 14 a is outmost and apressure channel 17 a leads to it by means of which channel the piston14 a can be pushed forwards. The piston 14 a stops at an abutmentsurface 15 a in the frame, whereby when the piston is in that positionand when the shank 2 is supported by the piston 14 a, it is at itsoptimal percussion point. The piston 14 b is coaxially inside the piston14 a and behind it pressure fluid enters along a channel 17 b. Thepiston 14 b also has a projection 14 b′ extending to the supportingsurface 14 a′ in the front of the piston 14 a in such a manner that thepiston 14 a can push the piston 14 b towards the front end of the shank.The piston 14 b pushes the shank with the help of the bushing 3.Correspondingly, when the shank 2 pushes the piston 14 b backwards, itis pushing the piston 14 a by means of its projections. Furthermore, thetravel of the piston 14 b towards the front portion of the drillingmachine is restricted by an abutment surface 15 b, whereby when thepiston 14 b is against the abutment surface 15 b, the shank 2 is at anew percussion point differing from the optimal percussion point.

In a normal situation, the pistons 14 a and 14 b are as shown in thefigure when the shank is at the optimal percussion point. If thepressure behind the piston 14 b is added through the channel 17 b, thepressure will, when it rises high enough, cause a force exceeding thefeed force of the drilling machine and move the shank and the drillingmachine with respect to one another in such a manner that the shank 2 isin the front of its normal percussion point.

This embodiment can be realized in different ways, whereby there may bea separate transmission ring or separate pins that transmit power fromthe piston 14 b to the bushing 3. Similarly, the pistons 14 a and 14 bcan be in the way shown in the figure or in the opposite way in such amanner that the piston 14 b is outermost and the piston 14 a isinnermost. Further, the pistons may also be one after the other in theaxial direction of the shank. Similarly, several pistons may beannularly concentric as shown in the figure and cylindrical pistons ofFIG. 1 can also be used at the same time as and in addition to annularpistons.

FIG. 4 shows a schematic view of forces caused in connection with oneembodiment of the invention by pressure changes when drilling upwardswith long hole drilling. The force shown with a horizontal line FS inthe figure is caused by the pressure behind the pistons 4 a, 14 a whichsupport the shank at its optimal percussion point. Stepped line FCdescribes the sum of the forces caused by means of the pressure setbehind the pistons 4 b to 4 d, 14 b which are capable of moving towardsthe front end of the drilling machine during drilling. Whenever onedrill rod is added to the drill rod set, the pressure behind the pistons4 b to 4 d, 14 b is raised in such a manner that the addition of mass iscompensated by the addition of pressure and thus the drill bit issupported in the front of the percussion point essentially with aconstant power. The sum of the force caused by the pressures behind thepistons 4 a; 14 a and 4 b to 4 d; 14 b, respectively, is greater thanfeed force and thus it is able to retain the shank at the optimalpercussion point, but the sum of the forces caused by the pistons 4 b to4 d; 14 b remains to be at a smaller value than the feed force of thedrilling machine. The feed force is described by broken line FF, wherebythe feed force is kept at the beginning of drilling so small that thesum of the forces caused by the pistons 4 b to 4 d moves the shankforwards and the percussion piston strikes the absorber. In thissituation, as shown in the figure, the force caused by the piston 4 dstays on to support the drill bit in the front of the percussion pointand enables the drilling to be controlled. Percussion power can thus beadjusted until drilling has started and normal drilling has begun. Onthe other hand, it happens sometimes in connection with normal drillingthat rock is soft or broken, which can be seen in the figure when brokenline FF falls abruptly and rises up after that at point A. In thissituation, the active force of the pistons 4 b to 4 d; 14 b exceeds thefeed force, whereby the shank penetrates into a new percussion point andthe percussion piston strikes the absorber and the percussion power willdiminish until ordinary rock is reached. When adding drill rods, thefeed force is also added to compensate for the mass, whereby a steppedline is formed as shown in the figure.

Point B is in a situation where the drill rod has started to resonate orit is known to resonate. In this situation, the force pushing thepistons 4 b to 4 d forwards is adjusted to be greater than the feedforce by adjusting the pressure. Here the travel of the pistons 4 b isrestricted in such a manner that the movement of the shank forwards doesnot move the percussion piston to the absorber at the end of the strokeso that the percussion power will not change essentially. As a result ofthe moving of the shank, the percussion length of the percussion pistonand thus the frequency of percussion change and resonance is thusavoided. On the other hand, the pressure level of the pistons 4 c andpossibly of the piston 4 d and the force caused by it is raised at thesame time so that bit contact, that is, supporting force in the front ofthe percussion point remains essentially unchanged. After adding one ormore drill rods, a normal pressure level and thus the optimal percussionpoint of the shank for the stroke can be regained. Also, the pressureacting behind the pistons and retaining the shank at its normalpercussion point can be adjusted by the number of the drill rods to beused, whereby straight line FS will be stepped in such a manner that therecoil receiving difference force of the piston force and the feed forceis constant, for example.

FIG. 5 shows a schematic view of the embodiment of the inventioncorresponding to FIG. 3 in other respects but that a uniform pressureacts there behind the pistons 14 a, 14 b at the same time. In that case,the adjustment of the percussion point of the shank 2 and percussionadjustment is carried out only by adjusting the pressure of the pressurefluid acting through the channel 17 a, an increase of which pressurewill make the piston 14 b to push the shank 2 forwards. In addition,this embodiment comprises separate transmission parts 18 between thepiston 14 b and the bushing acting on the shank 2 for transmitting powerforwards from the piston 14 b to the bushing 3 and further via thebushing to the shank 2.

The invention has been described and shown in the description above andthe drawings only by way of example, and it is in no way restricted tothis example. Different automatic pressure adjustment methods andapparatuses can be combined, when desired, to the method according tothe invention for attaining automatic power adjustment. Similarly, thesame, pressure can be fed behind all the pistons, whereby the requiredtransfer of the shank forwards requires a sufficient pressure withrespect to the number of the pistons which are capable of movingforwards. The pistons can be, as shown in drawings, of a singleitcomprises at least two pistons, pressure channels separate from oneanother leading to the pressure spaces behind the pistons and means forfeeding pressure fluid to the pressure spaces behind the pistons in sucha manner that a pressure is acting on them irrespective of one anotherconstruction but also different piston constructions which have betweenthe piston portions and the shank separate piston portions and differenttransmission bushings and bearing portions through which the pistons acton the shank mechanically and push it forwards.

What is claimed is:
 1. A method for adjusting drilling of a drillingmachine, said drilling machine comprising a frame, a percussion pistonsupported in the frame for movement along a longitudinal axis, anabsorber disposed at a front end of travel of a piston portion of thepercussion piston so as to be contacted by the piston portion at thefront end of travel of the piston portion, a shank supported in theframe in axial extension of the percussion piston so as to be impactedby said percussion piston in a working stroke thereof and at least twocontrol pistons supported in the frame for longitudinal movement, saidcontrol pistons being disposed in cylinder spaces arranged around thelongitudinal axis for moving the shank longitudinally to a selectedpercussion point at which the percussion piston impacts against theshank, said method comprising: applying pressure to each respectivecontrol piston to produce a respective stroke of each control piston,regulating the stroke of each respective control piston so that thecontrol pistons have respective strokes, which are different from oneanother, to move the shank to corresponding different respectivepercussion points, and moving the shank to said different selectedpercussion points by the respective control pistons by introducingpressure medium into said cylinder spaces at respective differentcontrolled pressures so that the control pistons move the shank torespective percussion points in accordance with the strokes of saidpistons whereby the shank is movable to a number of selected percussionpoints by the different control pistons.
 2. A method as claimed in claim1, comprising moving the shank to an optimum percussion point by a firstof said control pistons and moving the shank by a second of said controlpistons to a different percussion point.
 3. A method as claimed in claim2, comprising arranging the control pistons in first and second groupseach respectively including said first and second pistons and supplyingthe cylinder spaces of the control pistons in each of said groups withpressure medium at the same pressure within each group, the pressure ofthe pressure medium in the first and second groups being different fromone another.
 4. A method as claimed in claim 2, comprising transmittingforce from the control pistons to the shank, to move the shank, via abushing interposed between the control pistons and the shank, thebushing being slidably supported in the frame for movement in thelongitudinal direction.
 5. A method as claimed in claim 2, wherein whenthe shank is moved by said second control piston from said optimumpercussion point to said different percussion point, the percussionpiston impacts against the shank with a reduced impact force.
 6. Amethod as claimed in claim 2, wherein the shank is moved by said secondcontrol piston a sufficient distance away from said optimum percussionpoint, so that the percussion piston undergoes an increased stroke andstrikes the absorber.
 7. A method as claimed in claim 1, wherein anumber of drill rods are utilized in drilling depending on hole length,and the method further comprises adjusting the percussion point of theshank by the control pistons depending on the number of drill rods.
 8. Amethod as claimed in claim 1, wherein the pressure of the medium appliedto the control pistons is sufficiently high so that a force applied bythe control pistons to the shank is greater than a feed force of thedrilling machine.
 9. A drilling machine comprising a frame, a percussionpiston supported in the frame for movement along a longitudinal axis, anabsorber disposed at a front end of travel of a piston portion of thepercussion piston, so as to be contacted by said percussion piston in aworking stroke thereof, a shank supported in the frame in axialextension of the percussion piston so as to be impacted by saidpercussion piston in a working stroke thereof, and an axial bearingarranged in the frame for receiving axial forces applied to the framevia the shank during a drilling operation, said axial bearing comprisingat least two control pistons supported in the frame for longitudinalmovement, said control pistons being disposed in cylinder spacesarranged around the longitudinal axis for moving the shanklongitudinally to respective selected percussion points at which thepercussion piston impacts against the shank, said cylinder spaces ofeach of said at least two control pistons being connected by respectivepressure channels to receive pressure medium from different pressuresources at different pressures to produce respective strokes for saidcontrol pistons to move the shank to respective selected percussionpoints, at least a first of said control pistons having a length ofstroke to move the shank to an optimum percussion point at which amaximum impact force is applied to the shank by the percussion piston,and at least a second of said control pistons having a greater length ofstroke than that of said first control piston to move the shank awayfrom said optimum percussion point to another percussion point at whichthe impact force of the percussion piston on the shank will be reduced.10. A drilling machine as claimed in claim 9, wherein the shank is movedsufficiently far from said optimum percussion point by said secondcontrol piston that a stroke of the percussion piston is such that thepercussion piston impacts against said absorber and reduces impact forceon the shank.
 11. A drilling machine as claimed in claim 9, wherein saidcontrol pistons are arranged in a plurality of groups, the controlpistons in each group being connected to receive the same pressure ofthe pressure medium, the pressure of the pressure medium to therespective groups being different.
 12. A drilling machine as claimed inclaim 9, wherein a number of other of said control pistons displace theshank successively greater distances away from said optimum percussionpoint.
 13. A drilling machine as claimed in claim 9, comprising abushing between said control pistons and said shank to transmit forcebetween said control pistons and said shank.